Mixxx is software for DJs that provides everything needed to create live mixes. It allows you to beatmatch songs and crossfade them together, like you would with turntables and a mixer. It runs without any extra hardware, and offers a wide range of advanced features including comprehensive MIDI controller and vinyl control support. To obtain the lowest latency and highest responsiveness, it uses hardware video acceleration and takes advantage of multi-core CPUs.
Randomplay allows you to play your music collection in random order with a memory of songs played preserved across sessions, so you don't "lose your place" if you have to shut down. It also has many features to make command-line music playing more convenient, including recursive regexp searching for tracks and the ability to specify a certain number of tracks, bytes, or minutes to play. It can also generate a list of music files to be loaded onto a portable music player device.
mpgfe is an ncurses front-end to mpg123 with mouse support via GPM, advanced playlist editing features (load/save/add playlists in m3u format, order/shuffle a playlist, move/add/delete playlist entries), and resizing support. An interesting feature is the ability to display the lyrics of the song that is playing (provided that you added the name of the lyrics file after the song file. Song information is displayed while playing, in a customizable format. Volume control is available (both channels at a time) and also movement. You can display the length of every song and total playing time. The super user may run the player with real-time priority (playing will not be interrupted by disk access).
Music Manager is a Konqueror plugin that lets you standardize the filenames of your music files, guess information and set ID3 tags from the file's name (this can be done to several files in one shot), rename many selected files based on their ID3 tags, set ID3 tags in mass for selected files with options for copying ID3s from other files and leaving some ID3 fields untouched, rename _ to space and vice versa, create HTML and text indexes of your collections (including total playing time, etc., configurable through templates), create nice CD covers with full listings of your music files (also configurable through templates), and organize your music collection to create a CD.